Mechanical part of the grand organ (4)
I believe the answer is:
gear
'mechanical part' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'the grand organ' is the wordplay.
'the grand' becomes 'g' ('G' can be a synonym of 'grand').
'organ' becomes 'ear' (ear is a kind of organ).
'g'+'ear'='GEAR'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for gear that I've seen before include "Set of wheels working by engaging cogs" , "Cogwheel - equipment" , "Clothing - tackle" , "Equipment, clothing, goods" , "illegal drugs" .)